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#fluid dynamics

50 public questions tagged with this topic.

PHYSICS

A sphere of radius 0.025 m moves at 0.08 m/s through blood ( eta = 2.7 × 10⁻³ Pa s ). What is the viscous drag force

Given: A sphere of radius 0.025 m moves at 0.08 m/s through blood ( eta = 2.7 × 10⁻³ Pa s ). What is the viscous drag force? These values define the system as per NCERT data. Formula: Stokes’ law: F = 6 π eta a v. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: eta = 2.7 × 10⁻³ Pa s, a = 0.025 m, v = 0.08 m/s . F = 6 × 3.14 × 2.7 × 10⁻³ × 0.025 × 0.08 = 1.017 × 10⁻⁴ N . Result: The computed value matches the expected outcome and confirms the correct choice. Units and powers like J kg⁻¹ K⁻¹, m/s², 10⁻⁵ are pr

Ref: NCERT Physics Textbook for Class XI and XII, Chapter: Laws of Motion, Work Energy Power, Gravitation and System of Particles, Topic: Newton's laws, work-energy theorem and rotational dynamics.

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PHYSICS

A hole is made 1.2 m below the surface of a tank open to the atmosphere. What is the efflux speed? (Take g = 9.8 m/s² )

Given: A hole is made 1.2 m below the surface of a tank open to the atmosphere. What is the efflux speed? (Take g = 9.8 m/s² ) These values define the system as per NCERT data. Formula: Torricelli’s law: v = sqrt2 g h. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: g = 9.8 m/s², h = 1.2 m . v = sqrt2 × 9.8 × 1.2 = sqrt23.52 approx 4.85 m/s . Result: The computed value matches the expected outcome and confirms the correct choice. Units and powers like J kg⁻¹ K⁻¹, m/s², 10⁻⁵ are properly used as per NCERT.

Ref: NCERT Physics Textbook for Class XI and XII, Chapter: Units and Measurements and Physical World, Topic: Dimensional analysis and fundamental principles.

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Fluid Pressure, Pascal's Law and Manometers

A plate of area 0.07m2 moves at 0.3m/s over a 0.5mm thick water film (η\=1.0×10−3Pa s). What force is required?

Viscous force: F = ηvAl. η = 1.0×10−3Pa s, v = 0.3m/s, A = 0.07m2, l = 0.5×10−3m. F = 1.0×10−3×0.3×0.070.5×10−3 = 1.0×10−3×42 = 0.042N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 0.042 N. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Surface Tension, Capillarity and Excess Pressure

A spray tube (10cm2) has 50 holes of diameter 0.9mm. If the flow speed is 2.5m/min, what is the ejection speed?

A1v1 = A2v2, v1 = 2.5m/min = 0.04167m/s, A1 = 10×10−4m2. Hole area: Ah = π(0.45×10−3)2, total A2 = 50×π×2.025×10−7≈3.181×10−5m2. v2 = 10×10−4×0.041673.181×10−5≈1.31m/s. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 1.3 m/s. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Surface Tension, Capillarity and Excess Pressure

Why does the pressure in a fluid decrease when its speed increases in a horizontal pipe?

Bernoulli’s principle states that in steady flow, an increase in kinetic energy (12ρv2) corresponds to a decrease in pressure energy, as total energy is conserved along a horizontal streamline. As per NCERT, applying relevant law/formula with correct units and sign convention leads to Because of energy conservation. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCBI Bookshelf, Ideal Gas Law: P1V1/T1 = P2V2/T2.

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Surface Tension, Capillarity and Excess Pressure

A spray tube (7cm2) has 35 holes of diameter 0.8mm. If the flow speed is 3.0m/min, what is the ejection speed?

A1v1 = A2v2, v1 = 3.0m/min = 0.05m/s, A1 = 7×10−4m2. Hole area: Ah = π(0.4×10−3)2, total A2 = 35×π×1.6×10−7≈1.759×10−5m2. v2 = 7×10−4×0.051.759×10−5≈1.99m/s. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 2.0 m/s. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Surface Tension, Capillarity and Excess Pressure

A sphere of radius 0.015m moves at 0.2m/s through water (η\=1.0×10−3Pa s). What is the viscous force?

Stokes’ law: F = 6πηav. η = 1.0×10−3Pa s, a = 0.015m, v = 0.2m/s. F = 6×3.14×1.0×10−3×0.015×0.2 = 5.652×10−5N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 5.65 × 10⁻⁵ N. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Surface Tension, Capillarity and Excess Pressure

Why does blowing over a piece of paper lift it upwards?

Bernoulli’s principle states that faster airflow above the paper reduces pressure, while slower air below maintains higher pressure, creating an upward lift due to the pressure difference. As per NCERT, applying relevant law/formula with correct units and sign convention leads to Due to lower pressure above from faster airflow. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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